For the first one the 2wd and 4x4 steering boxes are different,Only way to use a 2wd box is to do cross over steering which is not needed unless you have 4 to 6 inchs of lift.For number 2 i believe you have to change the whole front end from the firewall forward core support and all.I would rather swap the whole axle then just the gears from one to the other.And being a 4x4 you have to re gear the front axle to match the rears ratio.So if your going that far i would just buy new gears and have them installed if you don't know how to do it.Honestly i would just buy new 2 inch lift springs for the front and a rear shackle flip that will give you 2 and half inch lift in the rear.Look at
http://offroaddesign.com/catalog/2inchliftsystem.htm